1. Field of the Invention
The present invention relates to a bending machine, and particularly to a positioning apparatus for precisely positioning workpieces on the bending machine.
2. Description of Related Art
With rapid developments in manufacturing industry, the demand for precision components is constantly increasing. A mechanical manipulator is often used to feed workpieces to a workbench in a bending machine, instead of using manual feeding. In order to precisely positioning the workpieces in the workbench, the manipulator itself must be precisely positioned.
FIG. 4 shows a conventional positioning apparatus 10 behind a lower die 20 of a bending machine (not shown). The positioning apparatus 10 comprises two generally symmetrical positioning blocks 101. Each positioning block 101 comprises a shoulder 102 with a front surface 103. Two approaching switches 105 are respectively installed on mutually opposing sides of the two positioning blocks 101. Each approaching switch 105 extends slightly beyond the front surface 103 of the corresponding positioning block 101. A post 107 is formed on one of the mutually opposing sides of the two positioning blocks 101. The post 107 is adapted to prevent the two approaching switches 105 from contacting each other and generating an error signal.
In operation, a manipulator (not shown) takes hold of a workpiece (not shown) and puts it onto the lower die 20. Then the manipulator horizontally pushes the workpiece toward the positioning apparatus 10. When the workpiece contacts the approaching switches 105, the approaching switches 105 are moved backward. The workpiece is continued to be pushed by the manipulator. When front walls (not labeled) of the approaching switches 105 become coplanar with the front surfaces 103 of the positioning apparatus 10, the workpiece is blocked by the positioning apparatus 10 and is positioned in the bending machine (not shown) ready for bending. A sensor (not shown) electrically connected with the approaching switches 105 sends a signal to the manipulator indicating that the workpiece is positioned ready for bending. The manipulator thereupon stops pushing the workpiece.
The conventional apparatus has a number of shortcomings. The approaching switches 105 have a range of tolerance, such that the workpiece cannot be precisely positioned. Furthermore, when the positioning width of the workpiece is narrow or the shape of the workpiece is unusual, the two approaching switches 105 cannot be used simultaneously. This reduces the precision of positioning of the workpiece. Moreover, the approaching switches 105 are relatively expensive.
Accordingly, an object of the present invention is to provide a positioning apparatus which can precisely position a workpiece having a narrow positioning width.
Another object of the present invention is to provide a positioning apparatus which can precisely position a workpiece having an unusual shape.
A further object of the present invention is to provide a positioning apparatus which is inexpensive.
In order to achieve the above-mentioned objects, a positioning apparatus for a workpiece in accordance with the present invention comprises a base, a positioning block and a circuit. The base comprises a shoulder defining a screw hole therethrough. The positioning block comprises an upper block, and a lower block having a front surface. The upper block defines a shoulder hole, for extension of a bolt therethrough to engage in the screw hole of the base. The bolt thereby secures the positioning block on the shoulder of the base. Layers of insulator are compressed between the base and the positioning block, and between the base and the bolt. The layers insulate the base and the positioning block from each other. The circuit comprises a power source and a relay. The power source provides direct current voltage. The relay comprises a coil electrically connected between the power source and the positioning block, and a normal-open switch electrically connected between the power source and a manipulator which acts on the workpiece. When the workpiece contacts the front surface of the positioning block, the coil is electrified and the normal-open switch closes. The interface of the manipulator turns to high level. The manipulator starts its next programmed motion, leaving the workpiece in its correct position.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.